1. Field of the Invention
The present invention relates to a development device and an image forming apparatus including the same, and more particularly, to a development device using two-component developer and an image forming apparatus using the same.
2. Discussion of the Background
Electrophotographic image forming apparatuses such as copiers, printers, facsimile machines, plotters, multi-function machines, or the like typically include a development device and a transfer unit. The development device develops a latent image formed on a photoreceptor serving as a latent image carrying member into a visible toner image. The transfer unit transfers the toner image from the photoreceptor onto a recording medium (e.g., transfer sheet) to form an image on the recording medium.
At present, the development device develops latent images into toner images using either one-component developer or two-component developer. The one-component developer consists of magnetic or non-magnetic toner. On the other hand, the two-component developer includes toner and carrier particles for carrying the toner. The development device develops the latent image formed on the latent image carrying member with the developer including the toner and the carrier.
The developer is agitated and mixed inside the development device using the two-component developer, at which time the toner is charged by friction generated between the toner and the carrier and then electrostatically attracted to the electrostatic latent image formed on the latent image carrying member, thereby forming a toner image.
In general, the development device includes a magnetic developer carrier such as a development sleeve and an agitator such as an agitation paddle or an agitation screw to agitate and mix the developer. The developer magnetically carried on the developer carrier is supplied to the surface of the latent image carrying member carrying an electrostatic latent image to develop the electrostatic latent image into a toner image with developer. The agitator agitates and mixes the developer to generate the frictional charge between the toner and carrier, and then supplies the developer carrier with the developer. The developer whose toner has been consumed in the development process of the latent image on the latent image carrying member is collected to the development device.
In certain related-art image forming apparatuses, the toner and the carrier are agitated in a dedicated agitation mechanism solely for agitating provided separately from the development device, and the agitation mechanism can be installed and replaced independently of the development device.
More specifically, one known image forming apparatus includes a development device including a transport screw provided with an auger as an agitation sleeve. Toner can be supplied from the top of the screw or from an axial end portion of the transport screw so that the toner is poured on the transport screw.
It is to be noted that the toner included in the developer must be replenished periodically because it is consumed during the development process, and unless replenished the image density of the formed image declines. The amount of toner that is supplied is controlled by controlling a rotation amount of a supplying member that discharges the toner from a toner container to a developer container. That control, in turn, is executed based on readings from a detector such as a toner concentration sensor that measures the toner concentration in the developer. When the fresh toner thus supplied is poured into the developer container, the fresh toner is mixed with the carrier in the developer by the transport screw located close to the supplying member to maintain a constant toner concentration. At the same time, the toner is charged frictionally by such agitation, and the toner that is charged a predetermined amount by friction is supplied to the development sleeve.
In the above-described configuration, in the developer agitating process the toner is dispersed in the developer and is electrically charged by agitation due to the rotation of the screw auger while the supplied toner is conveyed to the developer carrier. However, when a large amount of toner is consumed and subsequently supplied to the developer container during replenishment, the screw auger may not adequately agitate the developer. Consequently, the toner may not be sufficiently dispersed and charged by friction.
Insufficiently charged toner may adhere to a non-image area, that is, an area in which an electrostatic latent image is not formed on a surface of the latent image carrying member, or scatter to other peripheral devices, thus degrading image quality.
Additionally, when the screw auger or paddle, which has a relatively small surface area, is used, the screw auger may not contact all of the developer, thereby causing insufficient dispersion and charging of the toner.
Accordingly, there is a need for a technology to efficiently agitate the developer to disperse the toner to sufficiently charge the toner triboelectrically without at the same time degrading the developer.